The present invention relates to a control for a load carrier for an industrial vehicle, and more particularly to a control for down movement of a load carrier.
Among the industrial vehicles, there is known a forklift truck which is equipped with a load carrier to which various kinds of attachments, such as a fork assembly, may be attached. The load carrier is slidably mounted to vertical guide masts of the forklift truck and liftable by extension of a lift cylinder. The lift cylinder is retracted to allow downward movement of the load carrier. A load carrier controlling system which the inventor has made an improvement on operates as follows: Manipulating a lift control lever to shift a lift control valve from a neutral position to an up position causes operating oil from an oil pump to be supplied to a lift cylinder, causing a piston to move in such a direction as to extend the length of the lift cylinder. During this movement, the piston displaces oil out of the lift cylinder. The oil displaced out of the lift cylinder returns to a reservoir tank in an unrestricted manner. Thus, the load carrier can be lifted quickly. When the load carrier has been lifted upto a desired height, what the operator has to do is to manipulate the lift control lever to shift the lift control valve back to the neutral position. Then, the supply of oil to the lift cylinder is cut off. If it is desired to lower the load carrier from the elevated position, what the operator has to do is to manipulate the lift control lever to shift the lift control valve to a down position. Then, the load carrier starts descending owing to the total weight of the load carrier itself and a load supported thereby, causing the piston to move inwardly into the lift cylinder, resulting in retraction of the lift cylinder. This movement of the piston causes a portion of oil to be displaced out of the lift cylinder. The oil displaced out of the lift cylinder passes through the lift control valve before reaching the reservoir tank. Since the discharge rate of oil from the lift cylinder determines a speed at which the load carrier is lowered, the operator has to regulate the discharge rate of oil by controlling the degree of opening defined by the lift control valve by skillfully manipulating the lift control lever so as to decelerate the load carrier sufficiently before the load carrier is lowered down to a desired height where the fork assembly is to be removed from a pallet under the load. This operation requires a skilled technique, however.
An object of the present invention is to improve a load carrier controlling system of the above type such that, without any skilled technique, a load carrier is smoothly decelerated before being lifted down to a desired height.